import java.io.IOException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class RefreshFilter implements Filter {
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
filter((HttpServletRequest) request,(HttpServletResponse) response, chain);
}
private void filter(HttpServletRequest request, HttpServletResponse response,
FilterChain chain) throws IOException, ServletException {
String requestURI = request.getRequestURI();
Cache cache = Cache.getInstance();
cache.increment(requestURI);
if(cache.isUpCount(requestURI)) {
response.getWriter().println("到达次数，不允许请求，请稍候再试");
return;
}
chain.doFilter(request, response);
}
@Override
public void destroy() {
}
@Override
public void init(FilterConfig config) throws ServletException {
}
//缓存
private static class Cache {
private static final ConcurrentHashMap<String, CopyOnWriteArrayList<Long>> map = new ConcurrentHashMap<String, CopyOnWriteArrayList<Long>>();
private static final long EXPIRE_TIME = 1000 * 20L;
private static final long CLEAR_TIME = 1000 * 2L;
private static final int MAX_REFRESH_COUNT = 20;
private static final Cache cache = new Cache();
private Cache() {
new Thread(new ClearCacheRunnable()).start();
}
public static Cache getInstance() {
return cache;
}
//增长指定URL的点击次数
public void increment(String key) {
CopyOnWriteArrayList<Long> list = map.get(key);
if(list == null) {
map.put(key, new CopyOnWriteArrayList<Long>());
}
map.get(key).add(new Long(System.currentTimeMillis()));
}
//是否到达指定数量
public boolean isUpCount(String key) {
CopyOnWriteArrayList<Long> list = map.get(key);
if(list == null) {
return false;
}
return list.size() > MAX_REFRESH_COUNT;
}
//清理过期数据线程
private static class ClearCacheRunnable implements Runnable {
@Override
public void run() {
while(true) {
try {
Thread.sleep(Cache.CLEAR_TIME);
clear();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
private void clear() {
for(String key : map.keySet()) {
CopyOnWriteArrayList<Long> list = map.get(key);
for(Long date : list) {
if(System.currentTimeMillis() - date > Cache.EXPIRE_TIME) {
System.out.println(list.remove(date));
}
}
}
}
}
}
}
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